Mulberry harbours


Duration:2 years


Country: Normandy, France

What did this project achieve?

Construct temporary floating harbours for the 1944 D-Day landings

The Mulberry harbours were floating artificial harbours designed and constructed by British military engineers during World War 2.

They were used to protect supply ships anchored off the coast of Normandy, north west France, after the D-Day landings of June 6, 1944.

Supply ships needed to sit in deep water and so couldn't come in close to the shore. The harbours were intended to protect the ships from storms and enemy attack.

The idea for floating harbours came from several people. Winston Churchill had suggested them as early as 1917.

Military chiefs became interested in the concept after a disastrous British attack on the German-controlled port of Dieppe, France in 1942.

The failed raid showed that the Allies needed a way to get supplies across beaches in the early stages of an invasion.

Two Mulberry harbours were built for D-Day. Mulberry A was constructed off Omaha Beach to supply US forces. Mulberry B was built off Gold Beach at Arromanches to supply British and Canadian troops.

Mulberry A was destroyed in a storm a few days after it was built. Mulberry B was operational for 10 months after the landings.

Difference the floating harbours made

In the 10 months after D-Day, Mulberry B was used to land over 2.5 million troops, 500,000 vehicles and 4m tonnes of supplies.

The harbour is credited by some historians with shortening the war by increasing the effectiveness of the Allied supply chain during the invasion.

Other experts point out that US troops at Omaha beach were still supplied despite the loss of Mulberry A.

How the work was done

Around 45,000 people in 300 engineering companies around the UK worked on the project.

Each Mulberry was designed to be about a mile long and stand about 30ft (9m) above sea level at low tide and 10ft (3m) at high tide.

The harbours consisted of around 6 miles (10km) of flexible steel roadways floating on steel or concrete pontoons.

The structures were protected by sunken caissons – massive chambers filled with water to keep them on the seabed.

Beyond the caissons were lines of scuttled ships and a row of floating breakwaters.

The harbours were a major work of civil engineering. The caissons alone used around 31,000 tons of steel and 1.5m yards (1.4m metres) of steel shuttering. They were built in hastily constructed dry docks in the Thames and Clyde rivers.

The caissons and other components of the harbours were pulled across the Channel by tugs and assembled off the French coast. They were operational within 12 days of the landings.


Piers for use on beaches: they must float up and down with the tide... don't argue the matter. The difficulties will argue for themselves.

Prime Minister Winston Churchill

memo written in 1942

Fascinating facts

'Mulberry' and names of all the D-Day landing beaches appeared in the Daily Telegraph crossword puzzle in the month before the invasion. This led to the crossword compiler, headmaster Leonard Dawe, being questioned by MI5 secret service officers. MI5 decided the appearance of the words was a coincidence.

Many years later one of Dawe's students revealed the teacher often asked for words for his puzzles from pupils in his classes many of whom lived near US military barracks.

The British laid pipelines across the Channel to get fuel to Allied forces for D-Day. The operation was called PLUTO - Pipeline Underwater Transportation of Oil.

PLUTO didn't start pumping until September 1944 - 3 months late. However, the system was supplying 4m litres of oil a day to troops by March 1945.

People who made it happen

  • Commissioner: Prime Minister Winston Churchill
  • Idea sometimes credited to British Vice-Admiral John Hughes-Hallett who called for floating harbours after the failed Dieppe attack of 1942
  • Civil engineer Hugh Iorys Hughes submitted plans for a floating harbour to the Royal Navy in 1942. Some of his ideas were tested for use in the Mulberry project
  • Allan Beckett of the Royal Engineers designed floating roadways for the harbours

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